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For freshwater aquaria, gravel is the most common substrate. To prevent damage to fish, gravel should not be sharp. Aquarium gravel can be as coarse as pea-sized or as fine as 1–2 mm. [1] It is available in a number of colors, and may be naturally colored or dyed, and may have a polymer seal to ensure it does not affect water chemistry. [1]
The Unified Soil Classification System (USCS) is a soil classification system used in engineering and geology to describe the texture and grain size of a soil. The classification system can be applied to most unconsolidated materials, and is represented by a two-letter symbol. Each letter is described below (with the exception of Pt):
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In a defined sequence, the key asks for the presence or absence of certain diagnostics in a certain depth range. In addition, the key asks for single characteristics, e. g., a certain clay content or a certain base saturation. The soil belongs to the first RSG, for which it fulfils the set of criteria.
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Marl has been used as a soil conditioner and neutralizing agent for acid soil [13] [17] and in the manufacture of Portland cement. [18] Because some marls have a very low permeability , they have been exploited for construction of the Channel Tunnel between England and France and are being investigated for the storage of nuclear waste .
The high moisture content results in wet and sticky clay texture. When the clay swells, the low saturated hydraulic conductivity prevents the vertical water infiltration to the deeper soil horizon. It leads to water perches above the claypan layer. [5] The water permeability is restricted in the claypan layer resulting in low soil aeration.
The soil moisture regime, often reflective of climatic factors, is a major determinant of the productivity of terrestrial ecosystems, including agricultural systems. The soil moisture regimes are defined based on the levels of the groundwater table and the amounts of soil water available to plants during a given year in a particular region.